Ok ill start off by telling you my problem. #1,3,7,2,and 6 plugs are just about perfect maybe a little on the lean side but here is the weird part I cant figure out #5,6, and 8 plugs are way rich.

Now I will tell you what i have. Its a 91 firebird with a .040 over sbc 350. It has a 144 B&M blower with a 4150 holley 750 double pumper jetted 73's in the front 74's in the back. I have a plug in the power valve because im not sure which power valve to get yet because of high vacume readings cruising down the road at 55mph "14inches of mercury sometimes more". I have a mallory unilite distributor with mechanical advace only. Volmaster 2 coil. New accel 8.8 mm 300+ race wires with pro sleeves. AC R44TS plugs. Early 70s 350 4 bolt main, 4 barrel truck heads. forged flat top pistons steel crank and good rods.

I have taken it out drove it 55 mph down the road then pulled off to the side of the road right after cruising and everytime i foul plugs 5,6, and 8. then i put 3 new plugs in their spots and this time hammer it through the gears and pull over and check again only to get the same results. 1,3,7,2,4 look great 5,6,8 fouled. The car doesnt seem to miss any and it pulls hard. Im getting about 5 pounds of boost at full throttle also. I blows carbination out the exhaust when i hammer it but is normal when im driving down the road. i pulled the plugs out and put the plugs in the wires out side of the motor and had a friend turn it over only to see that the fouled plugs making a bigger spark than the non fouled plugs.



What is this all about.. Any suggestions would be great!!

 

you can do a compression test but a "leakdown" test is critical here. I have seen compression tests show good when a leakdown test showed that cylinder as half dead. leak down test takes a second longer to complete than the compression test anyhow. It just takes a different tool. If the tests show good then consider getting to a chassis dyno with a W/B O2 to finetune your carb.

 

Yea something is fishy. I would do the leak down & see what you come up with. another thing to consider is maybe ignition. everything else is common, maybe you have some bad wires or plugs or something that is fouling things up (pun intended).

BW

 

Well thats exactly what i thought too. But the problem is i have brand new Mallory unilite mehanical advace only distributer, voltmaster 2 coil, new accel 300+ race wires with pro sleeves "which i have moved around and nothing changed", and have gone through several new ac r 44ts plugs in the cylinders that are fouling them.

 

<b>new accel 300+ race wires with pro sleeves</b>
Weeel keep in mind those "Race wires" arnt always the best.
I had some taylor 11MM wires, supposedly "the best" for anything. I also had a strange high speed miss, somtimes. just for fun i replaced them with some crap pep-boys 8MM wires... no more miss!

I know you dont have a miss, just try swapping around the wires see if a different plug fouls.
I have a similar blower setup, and have never run into that weird problem. the reason? My plugs are ALWAYS fouled! heh. i found that running colder plugs means more boost but also means hotter ignition. you may want to consider getting rid of mallory at some point and going MSD with a BTM or somthing. In fact I have a leftover MSD Blower ignition setup (MSD 6-BTM / Mechanical Advance magnetic pickup dist. / blaster2 coil) for sale now that I use all computer controlled crap. the BTM was $320 new, Distributor was $310 new (marine style/water proof) and the coil was like $60. its all pretty new, figure about 4000 miles on it all.

Email me if interested.

 

some ignition systems specify no solid core plug wires or else the system will fail to perform. somebody needs to get the plug wire companies and the ignition manufacturers together. the ignnition manufacturers dont seem to make that great of a plug wire themselves.

 

My buddy has the same basic setup on his 74 camaro. He had nightmares over carb problems. He finally got a Holley carb especially designed for blowers, ended every problem he had. We even sprayed 150 shot of NOS on top and ran awsome. We just bolted the carb, right out of the box, and has been working great for about a year. Just my .02 worth.

 

what carb did he buy

 

He used a Holley part #0-80576. Its kinda expensive, but well worth it! I kept the box for my old carb. Luckily it was still in the garage.

 

Im interested in running nitrous. what kit did he buy and how did it perform? did he ever run it at the strip?

 

We used a Top gun Nitrous System. After trying many different brands, we found this to be the best for our application. Best pass on 200 shot of Nitrous is a 10.60. But this involves a lot of tuning.

 

is that a 142 or a 177... and whats the "boost pulley" size, and does it put out that much boost as the pulley says it will?

my 355 needs a 7 PSI pulley to make 5 psi of boost. yours needs... ?

and what size engine lol. that helps a little.

 

What we are using is a stock ZZ4 crate engine with AFR heads. Boost is only 6 psi, thats why we can use so much NOS. The heads are 'out of the box' with 1.6 rockers. We have about 8.75:1 compression. Trans is a B&M 350 with a Hughes 300 stall for Nitrous. 3.73 gears with a 'built' 12 bolt. the blower is a 142. As you can see in the pic, we are using a separate fuel pump for the NOS. there are a lot of othe "little" things im probably forgetting. It took almost 6 months of tuning to get it this quick. (timing , spark plugs, fuel pressures............etc

 

Ok i tried something new last night. After asking questions and thinking about what might be happening inside my motor I decided to read my spark plugs a different way. This time i took it out Rammed it through the gears and then ran it up to about 6,000 rpm then turned off the key and coasted to the side of the road. What did i find? All the plugs where equally on lean side. Everyone of them even 5,6,and 8 that always fouled! Then i drove it back home. but i have to go through town low rpm "around 1500rpm it really doesnt like that much you can feel the cam surge the whole time" because of loud exhaust and bitchy neighbors. When i pulled it in the garage and checked them all again what did i find. same old same old 1,3,7,2,4 where burning good and 5,6, and 8 where rich again. It seems that the fuel mixture is loading up in the intake and it just happens to be that 5,6, and 8 intake runners are the places that it wants to sit. I had a friend follow behind me when i was doing the tests he says the first time i get on it it blows carbination"cleaning out the cylinders" but the next time its find "it hasnt had a time to load up" im going to buy one of those blower carbs that have manifold referenced powervalves so it wont go so lean when Iget on it. For now im going to jet up the carb some and try to get it so it wont burn so lean.

 

i can see that happening. problem is, will a blower carb fix it? im sorry to place my opinion here, but i dont think it will. the biggest advantage of a blower carb is, like you said, manifold ref. power valves. but what does that do?

it means you can run leaner main jets and have enrichment under boost, where and when you want it. yeah that will help, alot. even your MPG will come up a little. maybe a lot. but will it fix your problem?

<b>750 double pumper jetted 73's </b>
for that blower, without a power valve, thats slightly on the lean side as it is, under boost conditions. explains your "lean plugs" after "getting on it" somwhat. I had to use 78's to keep it happy without power valves on mine. then i called holley and they faxed me a "manifold ref. power valve mod" paper, so i could make my existing carb into a blower carb. well, I did, and put in a nice 6.5" in the front (for stoplight takeoffs) and a 3.5" in the secondaries (for close-to-WOT throttle positions). its a simple thing, a drill and some loc-tite was mostly what i needed. small bit though. i can walk you through it if you want. i still have the paper from holley... somwhere....

my point is, if your engine is really "loading up", those cylinders, which doesnt make sense at all with a blower, (you need a REALLY REALLY BIG CAM), since the blower perfectly atomizes and mixes up the fuel and air as it passes down (which explains the increase in fuel economy on the highway) there really is no place for fuel to sit, especially in a blower manifold that is so small. no, i dont think thats the problem. (unless you have a huge cam... with over 240* @ .050 on the intake side. which is NO WAY good for that blower. more like 220~* @ .050 for that blower.)

under heavy load your mixture is obviouselly igniting really well. do you have an MSD box? is it a BTM? before I got my BTM my plugs always came out black. if i tried to lean out the jets a little the car wouldnt even run right. so i had them as lean as possible, but plugs were always black. what fixed it? Well, like i said, before I had the MSD BTM6-AL, I had a mallory ignition. a real crappy one too. turns out it was the plugs themselves though...

you see, apparently, when i bought my plugs, somone recommended colder plugs for my "blower" applcation. i said yes, great idea. I went 2 steps colder.
well, i swapped them out for regular old NGK's... and my black plug problems went BYE BYE. the colder heat range was NOT keeping the plugs hot enough to finish off the mixture. even the BTM was having trouble with them...
say, you dont have cold plugs do you?

 

Ok first I would like to say thanks for your post! I dont mind hearing that I may be wrong thats how we learn. This is my first blower application and Im new to some of these things. Just when you get N/A figured out you try a blower! HAHA

Ok on to the good stuff. Number one I would like to hear how to manifold reference my carb and you can email me when you find the papers. Two I wasnt sure that the new carb would fix my problem I just knew that it would help mpg and the carb was a little better than mine. It has blueprinted metering blocks and a blueprinted hp mainbody. Solid floats and manifold reference powervalve. All for 450 bucks. But if i can take my carb and do the mod myself i will. I have a question about the power valve in the back i really never hear of ppl running them. This must inable you to run a little leaner on the secondaries. Next on this list is my ignition. Right now i have a new mallory unilite mechanical advanced only. Attached to that is a Voltmaster Mach II coil that will really through a spark. On the other end are a set of Accel 8.8mm 300+ race wires with Pro Sleeves "these things are great the pro sleeve really helps when the wires are close the the headers". I have ran Ac plugs mostly. I too found out that a colder plug was not the answer for my set up so I tried the the R44ts which are used pretty common with hei ignitions. That was doing the job for most of the plugs but the back three still fouled them. I jumped up to the R45ts and of course it made the fronts lean and still the back 3 were fouled. As for the jetting I know it is on the lean side with the power valve out. Im going to just the carb up today and try to get them to all burn good "instead of all lean" under heavy acceleration. My motor really falls on its face below 2000 rpm. My car is a stick and anything below 2000 rpm it wants to surge and buck. I have a real high rear gear and that doesnt help much either but I will be replacing it soon!

 

<b>My motor really falls on its face below 2000 rpm</b>

sounds like its over-cammed. my cam was 234/244 @ .050 and below 2500 rpms, it made no power. couldnt even spin the tires... with a blower.
its either over-cammed... or theres an ignition / induction problem. that could mean anything from valve issues to timing issues. whats your timiing? whats your cam's duration and LSA? whats the rear gear?

ALMOST sounds like its too far retarded. does your car heat up fast and stay sort of hot? too retarded will do that on a blower motor.

 

hey king can you reply to my new topic on manifold referenced powervalves!